title: Role of tissue-engineered artificial tendon in healing of a large Achilles tendon defect model in rabbits.
abstract: BACKGROUND
  Treatment of large Achilles tendon defects is technically demanding. Tissue engineering is an option. We constructed a collagen-based artificial tendon, covered it with a polydioxanon (PDS) sheath, and studied the role of this bioimplant on experimental tendon healing in vivo.
  
  
  METHODS
  A 2-cm tendon gap was created in the left Achilles tendon of rabbits (n = 120). The animals were randomly divided into 3 groups: control (no implant), treated with tridimensional-collagen, and treated with tridimensional-collagen-bidimensional-PDS implants. Each group was divided into 2 subgroups of 60 and 120 days postinjury (DPI). Another 50 pilot animals were used to study the host-implant interaction. Physical activity of the animals was scored and ultrasonographic and bioelectrical characteristics of the injured tendons were investigated weekly. After euthanasia, macro, micro, and nano morphologies and biophysical and biomechanical characteristics of the healing tendons were studied.
  
  
  RESULTS
  Treatment improved function of the animals, time dependently. At 60 and 120 DPI, the treated tendons showed significantly higher maximum load, yield, stiffness, stress, and modulus of elasticity compared with controls. The collagen implant induced inflammation and absorbed the migrating fibroblasts in the defect area. By its unique architecture, it aligned the fibroblasts and guided their proliferation and collagen deposition along the stress line of the tendon and resulted in improved collagen density, micro-amp, micro-ohm, water uptake, and delivery of the regenerated tissue. The PDS-sheath covering amplified these characteristics. The implants were gradually absorbed and replaced by a new tendon. Minimum amounts of peritendinous adhesion, muscle atrophy, and fibrosis were observed in the treated groups. Some remnants of the implants were preserved and accepted as a part of the new tendon.
  
  
  CONCLUSIONS
  The implants were cytocompatible, biocompatible, biodegradable, and effective in tendon healing and regeneration. This implant may be a valuable option in clinical practice.
authors.affiliation: Division of Surgery, Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Fars, Iran. dr.ali.moshiri@gmail.com
authors.forename: Ali
authors.initials: A
authors.lastname: Moshiri
authors.forename: Ahmad
authors.initials: A
authors.lastname: Oryan
authors.forename: Abdolhamid
authors.initials: A
authors.lastname: Meimandi-Parizi
mesh_terms: D020341:Absorbable Implants; D000125:Achilles Tendon / Q000293:injuries*; D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D001705:Bioprosthesis; D002417:Cattle; D003094:Collagen / Q000502:physiology*; D055119:Elastic Modulus; D008297:Male; D008855:Microscopy, Electron, Scanning; D011817:Rabbits; D011897:Random Allocation; D051381:Rats; D012038:Regeneration; D013708:Tendon Injuries / Q000601:surgery*; D013718:Tensile Strength; D023822:Tissue Engineering; D014945:Wound Healing / Q000502:physiology*
chemical_list: D003094:Collagen
keywords: DPI; DTEC; ICTs; IL; ITTC-PDSs; ITTCs; NCTs; SB; TRDEC; days postinjury; direct transitional electrical current; injured control tendons; injured treated tendons with collagen implant; injured treated tendons with collagen implant and polydioxanon sheath; interleukin; normal contralateral tendons; scale bar; tissue resistance to direct electrical current